1. Field of the Invention
The present invention relates in general to electronic circuits and in particular to reference voltage circuitry for use in switched-capacitor application and systems and methods using the same.
2. Description of the Related Art
The ability to process audio information has become increasingly important in the personal computer (PC) environment. Among other things, audio is important in many multimedia applications, such as gaming and telecommunications. Audio functionality is therefore typically available on most conventional PCS, either in the form of an add-on audio board or as a standard feature provided on the motherboard itself. In fact, PC users increasingly expect not only audio functionality but high quality sound capability.
One of the key components in most digital audio information processing systems is the Codec (coder-decoder) unit. Among other things, the Codec converts input analog audio information into a digital format for processing by a companion digital audio processor. The digital processor for example may support sample rate conversion, SoundBlaster compatibility, wavetable synthesis, or DirectSound acceleration, among other things. The Codec also converts outgoing signals from the audio processor from digital-to-analog format for eventual audible output to the user. The Codec may also mix analog and/or digital audio streams.
The digital to analog converters (DACs) and analog to digital converters (ADCs) found in a typical Codec operate from a reference voltage. Therefore, a reference voltage source must be provided whether it be external and coupled to the chip through a dedicated pin or on-chip, such as with a band gap reference. Even for inexpensive Codecs, the reference source must meet certain minimum criteria. Among other things, it must be small, low power consuming and have a good power supply rejection ratio (PSRR). Moreover, different DACs and ADCs often require the generation of different reference voltages. Therefore, the need has arisen for circuits and methods for generating reference voltages which not only meet the above performance criteria, but also allows for the scaling of the reference voltage with the DC value of the power supply voltage.